Post-transcriptional regulation of albumin gene expression in Xenopus liver

To clarify on what level of gene expression estrogen represses albumin synthesis in Xenopus hepatocytes, we have analyzed nuclear RNAs and the transcriptional rates in isolated nuclei. Since in nuclear RNA the quantity of albumin mRNA and its precursors does not change and the transcription remains constant during estrogen treatment, we conclude that a posttranscriptional control, possibly involving destabilization of cytoplasmic mRNA, is responsible for the repression of albumin synthesis by estrogen. This post-transcriptional control is in contrast to the well-known transcriptional induction of vitellogenin gene activity. The results can be reproduced in liver cube cultures thereby establishing that estrogen interferes directly with hepatic albumin synthesis. In these liver cube cultures albumin mRNA levels are reduced compared with the liver used to set up the culture whereas the transcription of the albumin genes is not influenced. This reveals another post-transcriptional control of hepatic albumin synthesis.